As a conventional liquid level detecting apparatus for detecting a liquid level of a liquid in a tank, JP-06-249697-A, for example, discloses an apparatus that detects the liquid level with an ultrasonic wave. Specifically, the apparatus is for installing in a fuel tank mounted on an automobile. In the apparatus, an ultrasonic wave generated by an ultrasonic oscillation device is transmitted in fuel to the liquid level, the ultrasonic oscillation device receives a reflection wave reflected on the liquid level, and the liquid level is calculated based on the detection result of the reflection wave.
Further, U.S. Pat. No. 6,941,808, for example, discloses another liquid level detecting apparatus that is integrally formed with a fuel pump, which is installed in a fuel tank to feed fuel outward from the fuel tank. In the liquid level detecting apparatus according to U.S. Pat. No. 6,941,808, one end of an arm is rotatably supported on a bottom portion of the fuel tank, and the other end of the arm holds an ultrasonic oscillation device, so that the arm and the ultrasonic oscillation device can be retracted in the fuel pump.
According to this construction, in installing the liquid level detecting apparatus in the fuel tank, the liquid level detecting apparatus is inserted through an opening portion formed in the fuel tank in a state that the arm and the ultrasonic oscillation device are retracted in the fuel tank. Then, by installing the fuel pump on a predetermined position in the fuel tank to come in contact with a bottom face of the fuel tank, the arm flips upward to be extended, to return the liquid level detecting apparatus to a predetermined service position.
Ordinarily, the liquid level detecting apparatus is installed in the fuel tank through the opening portion of the fuel tank that is provided for installing the fuel pump, to decrease the number of the opening portion formed on the fuel tank.
Recent vehicle design is diversified, to make the shape of the fuel tank from simple rectangular one to complicated three-dimensional one. Accordingly, relative positions of the liquid level detecting apparatus and the fuel pump in the fuel tank is also diversified.
However, in the liquid level detecting apparatus according to U.S. Pat. No. 6,941,808, the relative positions of the liquid level detecting apparatus and the fuel pump is limited, because the liquid level detecting apparatus has a construction to be retractable in the fuel pump. That is, the liquid level detecting apparatus according to U.S. Pat. No. 6,941,808 cannot be applied to an apparatus that is disposed distant from the fuel pump by a specific length or more.
Further, the liquid level detecting apparatus is formed to be retractable in the fuel tank, so that an outer size of the fuel pump increases, and the size of the opening portion of the fuel tank also increases.
Furthermore, in a case that the liquid level detecting apparatus is installed at a position distant from the conventional opening portion of the fuel tank, it is necessary to form a base of the liquid level detecting apparatus in a large size, to make it difficult to install the liquid level detecting apparatus through the opening portion into the fuel tank.